Transmission fluid



TRANSMISSION FLUID John M. Clark, Birmingham, Mich., assignor to Studebaker-Packard Corporation, a corporation of Michigan No Drawing. Application June 10, 1953, Serial No. 360,813

1 Claim. (Cl. 252-75) This present invention relates to transmission fluids and more particularly to an aqueous solution adapted to be employed in the hydraulic servomotor power systems or automatic transmission mechanisms of motor vehicles.

Fluids used in such hydraulic systems of motor vehicles preferably should have adefinite combination of properties, the most important of which is that they must have adequate lubrication characteristics to eliminate wear in the operative parts. It is also essential that such fluids not freezeor boil at normally anticipated operating temperatures, and yet have a heat rejection property suflicient to prevent overheating of the fluid and thereby the driven elements of the system. They should be essentially noncorrosive in regard to both the metallic and non-metallic components of the system and the working fluid must be relatively non-foaming and have a viscosity which permits free flow around the hydraulic system, preferably being so constituted as to retain a substantially constant viscosity, homogeneous texture, and be resistant to decomposition, solidification, and separation of the ingredients throughout the temperature range to which they are exposed.

Heretofore oil base transmission fluids have been used exclusively in hydraulic systems of automatic transmissions. Although certain disadvantages of the oil base fluids are well recognized, up to the present time it has been found that such oil base transmission fluid oflered the most practicable combination of properties for use in the hydraulic system of an automatic transmission. As distinguished from such oily fluids, the present invention relates to a water base transmission fluid having all of the desirable properties of an oil base fluid and in addition the aqueous fluid of this invention has incorporated therein properties constituting distinct advantages over the oil base fluids that are now generally used.

I have discovered that an improved fluid can be provided for use in the power transmitting hydraulic systems of motor vehicles for example by forming an aqueous solution of glycols containing suitable additions in solution in order to impart to the solution properties corresponding to the more desirable characteristics of the fluids heretofore used. In this following invention, the basic aqueous solution may be suitably modified with such additions without detracting in any way from its inherent usefulness.

The water base fluid forming the subject of this invention is preferably an approximate 50% solution, by volume, of ethylene glycol in water. Other glycols such as propylene, diethylene, or dipropylene glycol may be substituted for ethylene glycol in forming the aqueous glycol solution. This 50% by volume composition has been found to have particularly good properties with respect to its viscosity, heat transferability, stability, freezing, and boiling characteristics. It has adequate antifreeze protection to -40 F., and yet its viscosity remains relatively constant throughout the entire temperature range in which it is to be used.

Minor ingredients are added to this base solution in nited States Patetit O 2,751,355 Pa.tented June 19, 1956 made which impart to it a non-corrosive property. So-

dium nitrite, borax, and triethanolamine may be added to the solution as corrosion inhibitors and when these compounds are used either alone or in combination in the solution they render the aqueous base fluid substantially non-corrosive for all uses encountered in automotive hydraulic systems.

During a period of time in which the hydraulic system and transmission are idle, any corrosive tendency of the solution in its vaporous phase must be controlled. In order to render the solution substantially non-corrosive in its gaseous state, vapor phase corrosion exhibitors are added to the solution. Volatile organic amines such as cyclohexanolamine, dicyclohexanolamine and octyldecyl amine are adaptable as vapor phase corrosion inhibitors and when added alone or in combination render the solution essentially non-corrosive in its vaporous state. Other compounds suitable for use as vapor phase corrosion inhibitors are dicyclohexylammonium nitrite and quaternary ammonium salts.

An anti-foaming agent is added to the solution to impart non-foaming characteristics to the fluid. A suitable anti-foaming agent used in the preferred form of the solution consists of a silicone emulsion. Other anti-foaming agents such as butyl phosphate or organo silicon or other known compounds may be used to render the solution substantially non-foaming.

A composition found to be particularly suitable for an aqueous base transmission fluid consists of a 50% solution of ethylene glycol in water, .25 oz. per gallon of sodium oleate soap, .25 oz. per gallon sodium nitrite, 1 oz. per gallon borax, .005 oz. per gallon triethanolamine, .009 oz. per gallon silicone emulsion, and 2.5 oz. per gallon dicyclohexylammonium nitrite. In this approximate composition the aqueous base transmission fluid has been found practical and possessive of definite advantages over the present day oil base transmission fluids now generally used. The concentration of additives in this solution are generally the minimum amounts from an economic standpoint that yield satisfactory results.

The compositions of some typically satisfactory fluids are set forth in the following table. These examples, however, are not to be constructed as a limitation of the invention but only as illustrative of some of the compositions embraced by the present invention. It is readily seen that the selection and concentration of the minor ingredients may be varied without departing from the scope of the present invention.

Ethylene Glycol (Parts by Vol. Propylene Glycol (Parts by Vol.)

50 Water (Parts by Vol.) 50 45 55 5O 50 50 50 Sodium Oleate Soap Oz.

per gal.) 25 50 .25 25 25 .25 Sodium Nitrite (Oz. per

gal. 25 25 25 50 25 25 Borax (Oz. per gal.) l 2 2 1 1 Triethanolamine (O per gal.) .005 Silicone Emulsion (Oz.

perg Butyl Phosphate (Oz.

per gal.) .01

Dicyclohexylammonium Nitrite (Oz. pergal.).. 2.5 2.5 2.5 2.5 2.5

The preferred form of the Water base transmission fluid constituting this invention has an absolute viscosity to times lighter than the oil base transmission fluids generally used and has relatively small change in viscosity with temperature changes. This decrease in viscosity coupled with a substantially equivalent lubrication characteristic constitutes a definite advantage and advancement over oil base transmission fluids heretofore employed since the decreased resistance to flow improves the overall efliciency of the hydraulic system. Also, the higher specific gravity characteristic of the water base transmission fluid as compared to an oil leads to a higher pump efliciency than is generally attained with oil base transmission fluids.

Fluids employed in the hydraulic systems of automatic transmissions of motor vehicles become heated to relatively high temperatures during the working cycle of the operative parts of the transmission with which the fluid in the hydraulic system is associated. An essential element of the hydraulic systems heretofore employed in automatic transmissions is a coolant system. It is the function of this coolant system to lower the temperature of the transmission fluid in order to permit continued and eflicient operation of the automatic transmission. The aqueous base transmission fluid herein disclosed has a significantly higher heat rejection property than known oil base transmission fluids. As a result of the higher heat rejection property of the disclosed aqueous transmission fluid, the hydraulic system and automatic transmission will operate at a relatively lower temperature and the size of the coolant system may be decreased or it may in certain instances even be eliminated.

While I have disclosed my improved transmission fluid in several preferred compositions, it will be appreciated that the invention is by no means limited to the exact compositions set forth by way of example, the solution being susceptible of considerable variation in the selection and amounts of minor ingredients.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

A water base hydraulic fluid for use in automatic transmission systems for automobiles and the like consisting essentially of a solution of water and ethylene glycol, said solution containing approximately .25 oz. per gallon of sodium oleate soap, .25 oz. per gallon of sodium nitrite, 1 oz. per gallon of borax, .005 oz. per gallon of triethanolamine, and .01 oz. per gallon of butyl phosphate.

References Cited in the file of this patent UNITED STATES PATENTS 1,928,956 Tatter Oct. 3, 1933 2,382,698 Donlan Aug. 14, 1945 2,462,694 Walker V Feb. 22, 1949 2,521,402 Osborn Sept. 5, 1950 2,602,780 Zisman et a1. July 8, 1952 

